The present invention relates to an electronic timepiece having a voltage converter circuit whereby a different voltage from the battery voltage can be supplied to provide drive power for an electromagnetic transducer, and means whereby the supply of said different voltage is effectively performed irrespective of a high output impedance of the voltage converter circuit.
An electronic timepieces become of increasingly reduced size, it becomes ever more necessary to reduce the power consumption of these timepieces, so that it will be possible to utilize a battery of small size to provide power, while ensuring a sufficiently long lifetime for such a small size of battery. One method of achieving this objective, in the case of an electronic timepiece which utilizes an electromagnetic transducer consisting of a stepping motor to drive time display means, is to vary the level of the drive voltage applied to the electromagnetic transducer in accordance with particular operating conditions. Such operating conditions can include a need for a higher level of torque than is normally required from the transducer, such as when a calendar display mechanism is driven by the transducer to change the displayed calendar information. Other operating conditions can include an abnormal operating temperature, a drop in battery voltage, and so on. In the case of a timepiece having a display of days of the week and date information, provided by rotating days and date dials respectively, the load torque on the stepping motor is of the order of 0.1 gm cm, as measured at the minutes shaft of the timepiece, during normal driving of the hours and minutes display of current time. When the motor drives the days and date dials, however, the torque required is of the order of 0.3 to 0.5 gm cm (again, as measured at the minutes shaft). In order to provide a sufficient margin of torque to ensure reliable operation of the calendar display, it is usual practice in such a timepiece to provide the stepping motor with a torque of the order of 2 to 3 gm cm. In other words, a factor of safety of about 6 is allowed. This means, however, that during normal operation (i.e. when only the seconds, minutes and hours hands are being advanced), there is a factor of safety of the order of 20 to 30 provided. This results in an excessively high level of power being consumed by the motor during normal operation. Since the time during which the days and date dials are advanced is about 1/4 of a day, i.e. about 6 hours per day, inefficient utilization of the battery is achieved. This runs counter to the objective of providing a battery of smaller size, and therefor smaller capacity, to enable a timepiece of compact size to be manufactured.